Coating travelling webs



May 16, 1967 R. A. ROSE ETAL 3,320,086

COATING TRAVELLING WEBS Filed Dec. 12, 1962 Eve-woes MM @M W Mm 7 10% $MJ/z A 70 Me is United States Patent fifice Patented May 36, 1967 3,326,086 CGATING TRAVELLING WEBS Richard Arthur Rose and Cyril Howard Phillips, Bridgwater, Somerset, England, assignors to British Cellophane Limited, Bridgwater, England, a British com- Filed Dec. 12, 1962, Ser. No. 244,082 Claims priority, application Great Britain, Dec. 21, 1961, 45,838/ 61 2 Claims. (Cl. 117-63) This invention relates to coating travelling Webs with liquid surface coating compositions.

In the art of coating travelling webs, such as paper or films, with a liquid coating composition, it is known to apply an excess of coating composition to one side of the web and then to doctor the coating, that is to remove excess coating composition by means of an airknife. The air-knife consists of a sheet of air projected under pressure from a slot-shaped air nozzle at an acute angle on to the coated surface of the web while the web is supported on a suitable moving support which is usually a rotating roller. The nozzle is usually fixed so that the sheet of air strikes the Web at an angle of about 80 measured in the direction of travel of the web, or where the web is supported on a roller, at an angle of 80 to the tangent to the roller at the line of strike of the sheet of air. The air-knife doctoring method is particularly useful since it imparts a highly smooth finish to the coating.

If it is desired to coat both sides of the web it has previously been necessary to dry the first coated side before air-knife doctoring the second coated side so that the first coated side can be brought into contact with a suitable supporting surface without damage to the coating. If the first coated side is wet, the coating composition adheres to the surface thus fouling the surface and severely disrupting the smooth coating on the web.

Further, when the web is of a material which is sensitive to the liquid coating composition, for example regenerated cellulose film which has been coated with an aqueous coating composition, there is a strong tendency for the web to curl inwards from the edges particularly on drying so that great difi'lCllliiBS are experienced in attempting to thread and lead the web through a second coating stage. To minimise such curling, it is a known practice to leave an uncoated margin of about inch (0.6 cm.) along each edge of the web. This practice however is wasteful of the web material as it is later necessary to cut away the uncoated portions.

The present invention provides an improved method for coating a web on both sides with a coating composition employing an air-knife doctoring technique.

Accordingly, the present invention includes a method for coating a flexible travelling web with a liquid coating composition which method comprises coating a first side of the web with the coating composition, removing any excess coating composition from the first side of the web, then coating the second side of the web with the coating composition and removing any excess coating composition with an air-knife while supporting the web, first coated side downwards, on a smooth moving heated surface capable of substantially drying the coating applied to the first side of the Web before the web is removed from the heated surface.

The coating applied to the second side of the web will be partly dried during the passage of the web over the heated surface and complete drying of this coating and any further drying of the coating applied to the first side of the web which may be necessary, or fusing of the coating, may be effected by passing the coated web through a heated atmosphere, for example a heated chamber.

The coating composition may be applied to each side of the web by any of the conventional techniques such as skim coat'mg or coating by an applicator roller which itself dips into a bath of the coating composition. By using the method in accordance with the invention webs which tend to curl at the edges when coated on one side, particularly on drying, may be coated from edge to edge on both sides of the web, since the second coating is applied before drying of the first coating takes place and before substantial curling can take place.

Any excess coating composition may conveniently be removed from the first side of the web by means of an air-knife while the web passes over a supporting roller.

The method in accordance with the invention may be used for coating any flexible webs such as paper, films of cellulosic material such as regenerated cellulose, cellulose esters, cellulose others and other cellulosic derivatives and films of synthetic plastic materials such as polyethylene, polypropylene, polyamides, polyvinyl derivatives and the like.

The coating composition may include aqueous solu tions or dispersions of coating materials. The method in accordance with the invention is particularly useful for coating regenerated cellulose film on both sides with highly moistureproof, heat-scalable coating compositions comprising aqueous dispersions of vinylidene chloride copolymers prepared by copolymerising vinylidene chloride in the range between and 96 parts by weight with between 20 and 4 parts by weight of one or more copolymerisable ethylenically unsaturated monomers such as acrylonitrile, methacrylonitrile, alkyl esters of acrylic and methacrylic acid, phenyl methacrylate, cyclohexyl methacrylate, methyl vinyl ketone, vinyl chloride or vinyl acetate.

The present invention also includes an apparatus for coating a flexible travelling web with a liquid coating composition which apparatus comprises a coating means for coating a first side of the web, a doctoring means for removing excess coating composition from the first side of the web, a second coating means for coating the second side of the web with the coating composition, a movable smooth heated surface for supporting the web first coated surface downwards, an air nozzle supplied with air under pressure for providing an air-knife for removing excess coating composition from the second side of the web while the web is supported on the heated surface, the heated surface being heated sufficiently to cause the substantial drying of the coating applied to the first side of the web before the web is removed from the surface.

The doctoring means for removing excess coating composition from the first side of the web may be an air nozzle supplied with air under pressure to provide an air-knife.

The coating means are preferably applicator rollers and the movable smooth heated surface is preferably a polished metal drum heated internally by the circulation of a hot fluid or by an electric heater. The drum may conveniently have a chromium plated surface which is incapable of being stained or marked by coating compositions and which imparts a smooth finish to the coating on the first coated side of the web which lies in contact with the drum. The heat supplied to the drum should be sutficient to dry the coating on the first coated side of the web to the extent that when the web is withdrawn from the drum the coating strips cleanly from the drum surface.

As a means for coating webs on both sides with a smooth uniform coating, the method in accordance with the invention has the advantages of being simple, economic and occupying little space.

Following is a description by way of example of a method of carrying the invention into effect with reference to the accompanying drawing which is a diagrammatic side elevation of a coating apparatus.

Example Referring to the drawing, a web 1 (for example, cellulose film) is drawn from a supply roll 2, round a guiding roller 3 and is coated on one side from edge to edge with a coating composition (for example, an aqueous dispersion of a vinylidene chloride copolymer) by means of an applicator roller 4 dipping in a bath 5 of the coating composition. The coated web 1 is then drawn round a supporting roller 6 with the coated side on the outside and excess coating composition is removed from the coated side by means of an air-knife 7, which is essentially a sheet of air projected under pressure at a suitable angle (for example, about 80 to the tangent to the roller 6 measured in the direction of travel of the roller) from a slot-shaped air nozzle 8. The excess coating composition drains back to the bath 5. The web 1 is then coated on the other side from edge to edge with coating composition applied by a second applicator roller 9 dipping in a bath 10 and is led round a freely mounted rotatable drum 11 heated internally by circulating steam and having a highly polished chromium plated surface, with the first coated side next to the drum 11. Excess coating composition is removed from the second coated surface by a second air-knife 12 and drains back to the bath 10.

On the passage of the web 1 round the drum 11, the first coated side of the web 1 is substantially dried at least to the extent that the web 1 can be stripped from the drum 11 at a nip between the drum 11 and a roller 13 without the coating sticking to the drum surface. As the drum surface is highly polished, the coating on the side of the Web 1 next to the drum 11 is not smeared or otherwise deleteriously affected. The second applied coating on the outside of the web 1 is partly dried during the passage of the web 1 over the drum 11. The coatings on both sides of the web are then completely dried (or fused if required) by passing the web 1 through a drying chamber 14 before winding into a storage roll '15.

We claim:

1. A method of coating a flexible travelling web of cellulosic or synthetic plastic film with a liquid coating composition comprising an aqueous solution or dispersion of a synthetic polymer; which method consists essentially of coating a first side of the travelling web from edge to edge with the liquid coating composition whereby the first side is wetted; removing any excess coating composition from the first side of said web; then, while the coating on the first side is still wet, coating the second side of said web from edge to edge with said liquid coating composition; and removing any excess coating composition from said second side of the web by directing a blast from the nozzle of an air knife against said second coated side of the web while the travelling web is supported with the first coated side in close contact with a smooth heated surface to thereby substantially dry the coating applied to the first side of the web; and then removing said web from said smooth heated surface.

2. A method as claimed in claim 1 in which the liquid coating composition consists essentially of an aqueous dispersion of a vinylidene chloride copolymer prepared by copolymerising vinylidene chloride in the range between 80 and 96 parts by weight with between 20 and 4 parts by weight of at least one copolymerisable ethylenically unsaturated monomers.

References Cited by the Examiner UNITED STATES PATENTS 2,325,798 8/1943 Porter 1171ll 2,748,027 5/1956 Meier 117-161 2,762,720 9/ 1956 Michel 1l716l 2,819,984 1/1958 Ackerman 117161 2,919,205 12/1959 Hart l17--64 3,044,896 7/1962 Warner 11764 3,108,017 10/1963 Messwarb et al. 1l7.-161

. FOREIGN PATENTS 774,352 5/1957 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

S. W. ROTHSTEIN, M. LUSIGNAN,

Assistant Examiners. 

1. A METHOD OF COATING A FLEXIBLE TRAVELLING WEB OF CELLULOSIC OR SYNTHETIC PLASTIC FILM WITH A LIQUID COATING COMPOSITION COMPRISING AN AQUEOUS SOLUTION OR DISPERSION OF A SYNTHETIC POLYMER; WHICH METHOD CONSISTS ESSENTIALLY OF COATING A FIRST SIDE OF THE TRAVELLING WEB FROM EDGE TO EDGE WITH THE LIQUID COATING COMPOSITION WHEREBY THE FIRST SIDE IS WETTED; REMOVING ANY EXCESS COATING COMPOSITION FROM THE FIRST SIDE OF SAID WEB; THEN, WHILE THE COATING ON THE FIRST SIDE IS STILL WET, COATING THE SECOND SIDE OF SAID WEB FROM EDGE TO EDGE WITH SAID LIQUID COATING COMPOSITION; AND REMOVING ANY EXCESS COATING COMPOSITION FROM SAID SECOND SIDE OF THE WEB BY DIRECTING A BLAST FROM THE NOZZLE OF AN AIR KNIFE AGAINST SAID SECOND COATED SIDE OF THE WEB WHILE THE TRAVELLING WEB IS SUPPORTED WITH THE FIRST COATED SIDE IN CLOSE CONTACT WITH A SMOOTH HEATED SURFACE TO THEREBY SUBSTANTIALLY DRY THE COATING APPLIED TO THE FIRST SIDE OF THE WEB; AND THEN REMOVING SAID WEB FROM SAID SMOOTH HEATED SURFACE. 